The present invention is generally directed to a process for preparing organometallic compounds by means of attaching one or more organic substituents to a central metal-oxygen structure. More specifically, the present invention is directed to a process for substituting or functionalizing polyoxometalates, under mild reaction conditions using readily available reagents, in high yield. The present invention is further directed to novel functionalized polyoxometalates prepared by the present process.
Polyoxometalates (xe2x80x9cPOMsxe2x80x9d) are a unique class of metal-oxygen xe2x80x9cclustersxe2x80x9d or compounds, having multiple metal and oxygen atoms arranged in a cage-like structure, which are generally considered to have extreme versatility in terms of structural, electrochemical and photophysical properties. Additionally, their unique electronic, optical and magnetic properties, as well as high thermal robustness, have made them very attractive in a number of applications, including their potential use (i) as catalysts, (ii) in various medicinal applications, (iii) as sensor or (iv) in other forms of analysis.
The modification of POMs through substitution, such as by the covalent attachment of substituents (e.g., organic species), as a means by which to xe2x80x9cfine tunexe2x80x9d the various properties of these metal-oxygen clusters, has been the focus of research in the past. For example, many have attempted the direct functionalization of the hexamolybdate anion, [Mo6O19]2xe2x88x92 (the cation typically being a tetrabutyl-ammonium ion). (See, e.g., Y. Du et al., J. Am. Chem. Soc., 1992, 114, 346; W. Clegg et al., J. Chem. Soc., Chem. Comm., 1995, 455; J. B. Strong et al., Chem. Comm., 1997, 1137; J. Stark et al., Angew. Chem. Int. Ed. Engl., 1995, 34(22), 2547; J. Stark et al., J. Chem., Soc., Chem., Comm., 1995, 1165; H. Kwen et al., Angew. Chem. Int. Ed. Engl., 1999, 38(8), 1145; J. B. Strong et al., J. Am. Chem. Soc., 2000, 122, 639; A. Proust et al., Inorg. Chim. Acta, 1994, 224, 81; and, W. Clegg et al., Polyoxometalates: from Platonic Solids to Anti-Retroviral Activity, (M. T. Pope and A. Muller, eds., Kluwer, Dordrecht, 1994), 113; all of which are incorporated herein by reference in their entireties.) However, to-date, proposed processes have typically employed: (i) the use of phosphinimines (Equation 1, below), which are not readily accessible and which typically yield a mixture of mono- and multi-substituted products, even when the stoichiometry of the reaction is carefully controlled (see, e.g., A. Proust et al. and, W. Clegg et al., J. Chem. Soc., Chem. Comm.); (ii) the use of isocyanates (Equation 2, below) which, compared to the phosphinimines, typically enables better control of the reaction product, but which also requires strictly anhydrous reaction conditions, high reaction temperatures and relatively long reaction times (see, e.g., W. Clegg et al., Polyoxometalates: from Platonic Solids to Anti-Retroviral Activity; Y. Du et al.; and, J. B. Strong et al.); and, (iii) the use of aromatic amines (Equation 3, below) under high reaction temperatures, which provide only moderate yields, in part due to the great difficulty experienced in isolating the desired product (see, e.g., W. Clegg et al., J. Chem. Soc., Chem. Comm.).                                                         [                                                Mo                  6                                ⁢                                  O                  19                                            ]                                      2              -                                +                                    Ph              3                        ⁢            P                          =                                            NAr              ⁢                              xe2x80x83                            ⁢                                                ⟶                                                                                                              85                          xc2x0                                                ⁢                        C                                            ,                                              xe2x80x83                                            ⁢                                              48                        ⁢                                                  xe2x80x83                                                ⁢                                                  hr                          .                                                                                      ⁢                                          xe2x80x83                                                                                        Pyridine                  ⁢                                      xe2x80x83                                                              ⁢                                                [                                                            Mo                      6                                        ⁢                                                                  O                        18                                            ⁡                                              (                        NAr                        )                                                                              ]                                                  2                  -                                                      +                                          Ph                3                            ⁢              P                                =          O                                    (        1        )                                                      [                                          Mo                6                            ⁢                              O                19                                      ]                                2            -                          +                  ArNCO          ⁢                      xe2x80x83                    ⁢                                    ⟶                                                                                          110                      xc2x0                                        ⁢                    C                                    ,                                      xe2x80x83                                    ⁢                                      2                    ⁢                                          -                                        ⁢                    3                    ⁢                                          xe2x80x83                                        ⁢                    days                                                  ⁢                                  xe2x80x83                                                                    Pyridine              ⁢                              xe2x80x83                                              ⁢                                    [                                                Mo                  6                                ⁢                                                                            O                                              19                        -                        x                                                              ⁡                                          (                      NAr                      )                                                        x                                            ]                                      2              -                                      +                  CO          2                                    (        2        )                                                      [                                          Mo                6                            ⁢                              O                19                                      ]                                2            -                          +                              ArNH            2                    ⁢                      xe2x80x83                    ⁢                                    ⟶                                                150                  xc2x0                                ⁢                C                                                                    PhCN                ,                                  xe2x80x83                                ⁢                                                      Et                    3                                    ⁢                  N                                            ⁢                              xe2x80x83                                              ⁢                                    [                                                Mo                  6                                ⁢                                                      O                    18                                    ⁡                                      (                    NAr                    )                                                              ]                                      2              -                                      +                              H            2                    ⁢          O                                    (        3        )            
Accordingly, a need continues to exist for a process which enables the preparation of substituted or functionalized POMs in high yields, by means of a process which is comparatively easy to perform; that is, a need continues to exist for a process whereby POMs may be functionalized under relatively mild reaction conditions and using readily available reagents, thus enabling a wide-range of substituted POMs to be prepared in high yields. In addition, a need continues to exist for such a process which enables a higher productivity to be achieved.
Among the several features of the present invention, therefore, may be noted the provision of a process for preparing organically substituted or functionalized polyoxometalates, as well as polyoxometalates obtained therefrom; the provision of such a process which enables the economical production of such substituted polyoxometalates; the provision of such a process wherein the substituted polyoxometalates are prepared under mild reaction conditions, including low temperatures and atmospheric pressures; the provision of such a process wherein the substituted polyoxometalates are prepared with a high productivity; the provision of such a process wherein commercially available reagents are employed, enabling a wide-range of substituted polyoxometalates to be prepared; the provision of such a process wherein the substituted polyoxometalates are prepared cleanly and in high yields; the provision of such a process which may be carried out in air and/or in the presence of moisture; and, the provision of such a process which enables functionalized polyoxometalates to be prepared having functionalities that may undergo further reaction or modification in a particular reaction of interest using common synthetic organic chemistry techniques.
Briefly, therefore, the present invention is directed to a process for preparing a polyoxometalate having an amine-derived substituent attached thereto.
The process comprises contacting a polyoxometalate and an amine in the presence of a diimide.
The present invention is further directed to an arylamino-substituted polyoxometalate compound which has an average composition of the formula: 
wherein: (MaOb-d) represents the average composition of the metal-oxygen cluster portion of the substituted polyoxometalate, the substituted polyoxometalate comprising one or more metals, M, which may be the same or different, selected from molybdenum, tungsten, vanadium, niobium, tantalum or a combination thereof; and, O is oxygen; N is nitrogen; R1 is a substituent selected from the group consisting of substituted or unsubstituted iodoarylene, alkynylarylene, N-alkylaminoarylene and N,N-dialkylaminoarylene; a represents the number of metal atoms; d represents the number of amine-derived substituents on the polyoxometalate; b-d represents the number of oxygen atoms, the number of oxygen atoms decreasing as the number of amine-derived substituents increases; and, q represents the net charge of the substituted polyoxometalate.
The present invention is still further directed to a process for preparing a bridged polyoxometalate reaction product, wherein two or more metal-oxygen clusters are linked. The process comprises contacting a first reactant polyoxometalate and a second reactant polyoxometalate, each having a substituent which does not comprises a metal-oxygen bond with the reactant polyoxometalate, the substituent on the first reactant polyoxometalate being different from the substituent on the second reactant polyoxometalate, the two reactant polyoxometalates being contacted in the presence of a catalyst capable of catalyzing a coupling reaction between the two different substituents.
The present invention is still further directed to a process for preparing a polyoxometalate having an amine-derived substituent attached thereto. The process comprises contacting a reactant polyoxometalate, a reactant primary or secondary amine, and a reactant activating compound which bonds with a terminal oxygen of the reactant polyoxometalate, forming a leaving group therewith.
The present invention is still further directed to a process for preparing a polyoxometalate having an amine-derived substituent bound thereto. The process comprises contacting a polyoxometalate and an amino-substituted diimide.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.